1. Field of the Invention
The invention relates to a cartridge for a paste-like substance, comprising a tubular cartridge body closed at its front by an end wall which is provided with an outlet nipple delimiting an outlet opening, and a plunger which is inserted into the open rear end of the cartridge body. The plunger lies sealingly against the inner wall of the cartridge body and, upon displacement towards the front end wall of the cartridge body, presses the substance through the nipple opening.
2. Related Art
Paste-like substances for which such cartridges are used include sealing compounds, such as adhesives or the like, which harden from exposure to air. Expressing of the substances from the cartridges may be effected by mechanical or pneumatic extraction pistols, in which a pressure ram or compressed air presses the plunger forward.
The cartridges are made of rigid plastic materials, usually polyethylene (HDPE). Empty cartridges have a relatively large volume, and are thus bulky to dispose of. Accordingly, it is desirable to avoid this problem by reworking the plastics material, such as by grinding the empty cartridges for subsequent recycling.
Here the problem arises, however, that with known cartridges, even when the substance is fully expressed therefrom, the remains a relatively large residual quantity of the substance in the cartridge, on the order of 10 g. To illustrate the problem, reference is made to FIG. 1 of the drawings, which shows in cross-section the front end of an expressed cartridge. The conventional convex shape of the plunger, because of the radial force component generated during the axial upsetting of the plunger, does admittedly facilitate trouble-free sealing with the cartridge body wall. However, when the plunger is pressed forward as far as it will go, a relatively large residual quantity (illustrated by the dark areas) of the substance is left in the spaces remaining between the cartridge body, front end wall, and the convex front face of the plunger. Moreover, a considerable quantity of the paste-like substance is left in the opening of the outlet nipple.
The residual substance leads to smearing of the mills and to clogging. A further and particularly aggravating factor is that the substance remaining in the spaces, even over an extended period of time, does not harden. That is, air is prevented from entering the cartridge since the plunger seals off the opening of the nipple, resulting in the substance being enclosed in an airtight manner in the spaces, thus remaining in a paste-like, i.e. extremely smeary and sticky, state. Grinding empty cartridges containing such non-hardened residual quantities rapidly renders the mills unserviceable.